Reasoning and Delusions

Delusions are among the most common psychiatric symptoms, but the psychological processes involved in their formation and maintenance remain a matter of controversy. This paper briefly reviews competing theories, particularly those involving abnormalities of perception and reason. An investigation of reasoning in deluded schizophrenic and paranoid subjects is presented, followed by a tentative model of belief formation in which abnormalities or biases in reasoning and perception, implicated in the formation of some delusions, are highlighted.